Manufacture of pyrrole derivatives



Patented Aug. 14, 1945 Ra oF rrnnonnpnarvA'rivss Maurice hrthunThorold Rogers, Blackley, Man- & chester, England, vassignor to1ImperialChemicallndustrie's liiinited, a

, Britain corporation of Great No Drawing. Application September3,1942, se rial No. 457,230. In Great Britain peceniber 17,

3 cranes (o1. 260-313) M This invention relates: to the m'anuiact new pyrrole derivatives, and in particularlitgrelates to the manufacture of -nitroso -2A-diarylpyrroles. 7,; 14,-.

According to the'inventioniprovide a process for the manufacture of 5 -nitroso-2z4-diarylpyrroles which comprises nitrosating a2z4-diarylpyrrole.

The nitrosating may be effected in a number of ways. It may be effected conveniently Joy-treatment of the 2:4-diarylpyrrole with nitrous acidor with a functional derivative thereon Thustlie 2:4-diarylpyrrole may conveniently be dissolved or suspended in a suitable liquid for example water or ethanol, and a mineral acid, for example hydrochloric acid may be then added; to this mixture an alkali metal salt of nitrous acid, for example sodium nitrite, may be added. Alternatively, there may be added to the acidified solution of the 2:4-diarylpyrrole an ester of nitrous acid, for example amyl nitrite. Or nitrosyl chloride may be added to the Zz l-diarylpyrrole dissolved in a suitable solvent. Or again the nitrosation may be brought about by treatment of the 2: l-diarylpyrrole with nitrosyl sulphuric acid such as may be obtained by dissolving sodium nitrite in cold concentrated sulphuric acid. The nitroso-compounds may be. isolated as the free bases or in the form of the corresponding salts, for example, the hydrochlorides.

The 2:4-diarylpyrroles which are the starting materials used in the invention may be obtained by the process described in copending application Serial No. 457,229 of even date herewith, namely, by the dehydrogenation of 2:4-diaryl-pyrrolines and -pyrro1idines.

As examples of suitable 2:4-diarylpyrroles there may be mentioned, 2:4-diphenylpyrrole, 2-(pmethoxyphenyl) -4-phenylpyrrole, 2-phenyl-4- (pmethoxy-phenyl pyrrole, 2- (m-hydroxyphenyl) -phenylpyrrole, 2- (o-chlorophenyl) l-phenylpyrrole, 2-(p-acetylaminophenyl) -4-phenylpyrrole, 2-anaphthyl-e-phenylpyrrole, 2-phenyl-4- fi-naphthylpyrrole, 2 3 Q-triphenylpyrrole, B-ben- ZOylamino-Z l-diphenylpyrrole, 3-acetylamino- 2 4-diphenylpyrrole, 3-benzoylamino-2 4-di-ptolylpyrrole and 3-acetoacetylamino-2:4-diphenylpyrrole. Also included are the sulphonic acids of the 2:4-diarylpyrroles, which may be made, for example by sulphonating the above compounds.

The nitroso compounds of this invention may be represented by the general formula wherein R and R. represent aryl radicals of the benzene and naphthalene series, while R" designates hydrogen, aryl or acylamino; however, in view of the double-bonds, it must be borne in ind that this formula is but one of several tautomeric configurations possible.

The invention is illustrated, but not limited, by the following examples in which the parts are by weight. i 1 Example 1 .1 5.0 parts of 2:4-diphenylpyrrole and 150 parts of alcohol are heated until the pyrrole is dissolved. The solution is then cooled With stirring, whereby much of the dissolved diphenylpyrrole is i e-precipitated as a fine crystal paste, and 5 parts or concentrated hydrochloric acid (sp. gr. 1.18) are then added. Into this suspension there is gradually introduced a solution of 1.8 parts of sodium nitrite in 20 parts or water.. The diphenylpyrrole is redissolved, and a dark yellow-brown solution is formed. The solution is filtered to remove any impurities, and 25 parts of concentrated hydrochloric acid (sp. gr. 1.18) are added, whereby the hydrochloride of 2:4-diphenyl-5-nitrosopyrrole is precipitated in the form of long brown needles, which are soluble in alcohol and in warm acetic acid, insoluble in benzeneand acetone.

If it is desired to make the nitroso base instead of the hydrochloride, there is added in place of the 25 parts of hydrochloric acid, 25 parts of sodium acetate dissolved in 50 parts of alcohol; the colour of the solution changes from deep brown to a greenish-yellow, and when the solution is diluted with 500 parts of water there is obtained a green solid, which is filtered off, dried and recrystallised Irom ether. 5-nitroso-2z4-diphenylpyrrole is obtaine in the form of green needles, M. P. 139-440 C.

Example 2 6 parts of the sodium salt of 2:4-diphenylpyrphenylpyrrole sulphonic acid which separates is collected by filtration and dried. It is soluble in aqueous alkali and in dilute aqueous ammonia.

Example 3 22 parts of 2:4-diphenylpyrrole are dissolved in 200 parts of concentrated sulphuric acid, and the solution is added slowly to a solution of 15 parts of sodium nitrite dissolved in 200 parts of concentrated sulphuric acid, the temperature being kept 5 C. by external cooling throughout the addition. The mixture is stirred during 1 hour below 5 C., and the solution is then poured on to 1000 parts or crushed ice. There is thus formed an orangeyellow precipitate, which consists of the sulphuric acid salt of 5-nitroso-2z i-diphenylpyrrole. The precipitate is collected by filtration and dried at 50 C.

In place of the 2:4-diphenylpyrrole there may be used 2-phenyl-4- (o-chlorophenyl) -pyrrole.

Example 4 orange precipitate of 5-nitroso-2:4 diphenylpyrrole hydrochloride which is collected by filtration and dried. 1

Example 5 23 parts of 2-phenyl-4-(p-methoxyphenyl)- pyrrcle are suspended in 500 parts of ethyl alcohol' and 5 parts of concentrated hydrochloric acid are added to the suspension. There is then added to the stirred mixture during 30 minutes 12 parts of amyl nitrite. The pyrrcle is thereby dissolved and a solution of deep purple colour is formed. To this solution there is added 50 parts of concentrated hydrochloric acid. There is thereby formed a precipitate of 5-nitroso-2-phenyl-4-(pmethoxyphenyl) -pyrrole hydrochloride. The precipitate is collected by filtration and dried. If

desired, it may be purified by recrystallisation from ethyl alcohol whereby it is obtained in the form of purple prisms.

I claim:

1. 5-nitroso-2 4-diphenylpyrrole.

2. A compound of the group consisting of the members having the formula hereinbelow and their tautomers, said formula being wherein R and R represent aryl radicals having not more than 10 carbon atoms in their cyclic structure, while R" represents a member of the group consisting of hydrogen, phenyl, and acylamino 3. A compound of the group consisting ofthe members having the formula hereinbelow and their. tautomers, said formula being wherein R and R represent benzenoid aryl radicals.

MAURICE ARTHUR THOROLD ROGERS. 

